fix(skills): remove phantom resource references and fix CoC links (#447)

Remove references to non-existent resource files (references/, assets/,
scripts/, examples/) from 115 skill SKILL.md files. These sections
pointed to directories and files that were never created, causing
confusion when users install skills.

Also fix broken Code of Conduct links in issue templates to use
absolute GitHub URLs instead of relative paths that 404.

plugins/ui-design/skills/visual-design-foundations/SKILL.md

@@ -316,11 +316,3 @@ export function Icon({ name, size = "md", className }: IconProps) {
 - **Magic Numbers**: Arbitrary values instead of tokens
 - **Missing States**: Forgetting hover, focus, disabled
 - **No Dark Mode Plan**: Retrofitting is harder than planning
-
-## Resources
-
-- [Tailwind CSS Documentation](https://tailwindcss.com/docs)
-- [Type Scale Calculator](https://typescale.com/)
-- [Contrast Checker](https://webaim.org/resources/contrastchecker/)
-- [Material Design Color System](https://m3.material.io/styles/color/overview)
-- [Radix Colors](https://www.radix-ui.com/colors)